1. Field of the Invention
The present invention relates to image processing for detecting a specified pattern such as a circular pattern in an image.
2. Description of Prior Art
Recently, a color copying machine provides more functions with improved performance, and counterfeit of paper money or the like becomes a big problem. Then, effective countermeasures for preventing counterfeit have been researched. In one of the countermeasures, specified patterns have been embedded in a design in a paper money or the like. When an image is read in copying operation in a copying machine, the scanned image is analyzed. When a specified pattern is recognized in the image, normal image forming is forbidden.
Input or output apparatuses such as a scanner or a printer available recently can process a large amount of image data such as high resolution data at higher speed. Then, it is required to cooperate with them in order to detect specified patterns in real time. Further, an image processor is demanded to detect the specified patterns in a shorter time.
A circular pattern is used as one of the specified patterns. The detection of a circular pattern is described, for example, in Japanese patent laid open publication 11-198631/1999, wherein specified pixels in a circular area are counted. However, the counting of the specified pixels in a circular area is more complicated than that in a rectangular area. For a circular pattern as the specified pattern, an image processor is demanded to detect it at higher speed.